This invention relates to a throttle valve control device for a vehicle engine.
A throttle valve control device is being developed as part of the engine control for improving the exhaust gas purifying performance and the economical use of fuel of an engine. In the throttle valve control device, the mechanical connection between the throttle valve and the acceleration pedal is eliminated, and instead an electronic control actuator is employed which controls the operation (opening and closing) of the throttle valve in response to both an electrical signal which is obtained by converting the amount of movement of the accelerating pedal (hereinafter referred to as "an accelerating-pedal movement signal", when applicable) and signals (such as an engine speed signal and a gear position signal) representing other engine operating conditions or vehicle running speeds.
In the conventional throttle valve control device with the electronic control actuator, the operation of the throttle valve is controlled by the drive motor which is operated in response to instructions signals from a vehicle controller, which comprises an arithmetic and control circuit adapted to calculate a most suitable degree of opening for the throttle valve according to the signals representing engine operating conditions and vehicle running conditions. Therefore, the device should be equipped with security means for preventing the occurrence of a difficulty that the operation of the vehicle becomes out of control when the electronic control actuator becomes out of order during traveling of the vehicle.
The following examples of the security means have been disclosed by Japanese Patent Application (OPI) No. 145867/1980 (the term "OPI" as used herein means "an unexamined published application"):
(1) In the first example, a return spring for returning the throttle valve to the closing position when the control is stopped is provided for the throttle shaft.
(2) In the second example, an electromagnetic clutch is provided to disconnect the throttle shaft from the electronic control actuator when the latter does not work.
(3) In the third example, the return spring and the electromagnetic clutch are combined together in such a manner that the return spring is operated in response to the disconnection of the electromagnetic clutch.
However, the above-described conventional throttle valve control device suffers from a drawback that, when the electronic control actuator becomes out of order, the above-described difficulty that the operation of the vehicle becomes out of order can be prevented; however, the vehicle cannot be run away any longer, so that the vehicle cannot be moved to a certain place for repair for instance.